Mechanism of labor in right occipito posterior position

Obstetrics

1. Mechanism of labor in right occipito -posterior position By: Gautam Hariish and Jenadia Naidoo

2. Occiput Posterior Position Occiput placed posteriorly over sacroiliac joint or directly over sacrum. Fetal face towards maternal symphysis pubis or anterior segment of pelvis More common in android and anthropoid pelvis

3. Mechanism of labor in ROP There are 2 mechanisms: Anterior rotation: Long arc (135°) Posterior rotation: Short arc (45°)

4. Mechanism in long arc ( 135 °) rotation Descent Head enters the pelvis with sagittal suture in the right oblique diameter. Descent continues throughout labor unless any obstruction is encountered.

5. Mechanism in long arc ( 135 °) rotation(continued) Engagement Engaging transverse diameter of the head is biparietal diameter. AP diameter is either: - Suboccipitofrontal due to incomplete flexion - Occipitofrontal due to marked deflexion

6. Mechanism in long arc ( 135 °) rotation(continued) Flexion I mperfect and often not complete till head reaches the pelvic floor. Partial flexion and the resulting larger diameter of the presenting part contributes to prolonged labor .

7. Mechanism in long arc ( 135 °) rotation(continued) Internal rotation Occiput is the leading part and rotates 135° anteriorly and lie behind the symphysis pubis. Neck cannot sustain such torsion, the shoulders rotate about 90° to occupy the right oblique diameter. (lag of 45°)

8. Mechanism in long arc ( 135 °) rotation(continued) Extension Head delivers by extension Nape of neck pivots under the sub pubic angle and the head is born in extension BREGMA  FOREHEAD  NOSE  CHIN (Pass over the perineum in this order .)

9. Mechanism in long arc ( 135 °) rotation(continued) Restitution After delivery of the head , it restitutes to the right from OA  ROA The extent d epends on the degree that shoulders have followed the head during internal rotation. In most cases, the shoulders lag by 45 °, so restitution is by 45 °.

10. Mechanism in long arc ( 135 °) rotation(continued) External rotation The anterior shoulder strikes the pelvic floor and rotates 45° towards the symphysis pubis. T he bisacromial diameter of the shoulders is in the AP diameter of the pelvic outlet. The birth of shoulders and trunk by lateral flexion.

11. Mechanism in short arc (45°) rotation Descent Head enters pelvic inlet with sagittal suture in the right oblique diameter of the pelvis. Descend continuous throughout labor.

12. Mechanism in short arc (45°) rotation (continued) Flexion It is imperfect resulting in longer presenting diameter.

13. Mechanism in short arc (45°) rotation (continued) Internal rotation As sinciput hits pelvic floor, it moves anterior. The occiput turns posterior by 45° ROP → OP into hollow of sacrum. Sagittal suture is in AP diameter of pelvis and bregma is behind pubis.

14. Mechanism in short arc (45°) rotation (continued) Birth of head by combination of flexion and extension Good flexion Incomplete flexion The area under the bregma pivots under the symphysis The root of nose pivots under the symphysis Presenting diameter: Suboccipitofrontal ( 10.5cm ) Presenting diameter: Occipitofrontal diameter ( 11.5 cm ) Bregma, vertex, small fontanel le s and occiput are born by further flexion Forehead, bregma , vertex and occiput are born by flexion Less traumatic More traumatic

15. Mechanism in short arc (45°) rotation (continued) Restitution The head moves 45 ° in the direction opposite to that of internal rotation. Face look towards mother’s left thigh in ROP.

16. Mechanism in short arc (45°) rotation (continued) External rotation Anterior shoulder strikes pelvic floor and rotates 45 ° towards symphysis pubis. This brings the bisacromial diameter to AP diameter of the pelvis. R esults in external rotation of head 45 ° to the right. Birth of shoulders and trunk by lateral flexion.

17. DEEP TRANSVERSE ARREST Incomplete forward rotation . Occiput rotates through 45 ° forwards . S agittal suture comes to lie in bispinous diameter . Further rotation unlikely. OBLIQUE POSTERIOR ARREST Non rotation . Both sinciput and occiput, touch the pelvic floor simultaneously due to deflexion of head . Sagittal suture lies in oblique diameter . Non Rotation or Malrotation

18. OCCIPITOSACRAL ARREST Due to extreme deflexion . S inciput touches pelvic floor & rotates anterior . This puts occiput in sacral hollow . Direct occipitoposterior or persistent occipito posterior position. Can deliver by face to pubis but arrest can occur Non Rotation or Malrotation (continued)

19. Consequences of OP position Prolonged 1 st and 2 nd stages of labor. High incidence of operative delivery. Increased chance of intervention such as ARM and oxytocin augmentation due to prolonged labor. Maternal trauma such as anal sphincter injury due to operative delivery.

20. Video link https://www.youtube.com/watch?v=7np77uatrbo

21. THANK YOU